Characterization of Crack Length Measurement Methods for Flat Fracture with Tunneling

James, MA
National Institute of Aerospace, Hampton, VA

Newman, JC
Mississippi State University, Mississippi State, MS

(Received 12 November 2003; accepted 11 March 2004)
JOURNAL JAI
Abstract
This paper compares area-average and unloading compliance crack-growth values with experimental crack-front shapes recorded at various stages of crack growth during fracture tests conducted on 2024-T351 aluminum alloy plate. Crack-front shapes were determined by fracturing the specimen up to a predetermined amount of crack growth and fatigue cycling the specimen for about 4000 cycles at a high stress ratio to mark the crack-front location. For each shape, the area-average and unloading compliance crack lengths were determined. Boundary collocation results provide an approximation to the d₅ unloading compliance crack length. The crack tunneling results show that the area-average technique produces crack-length measurements more representative of the straight-front finite element analyses than optical based surface measurements. The d₅ technique is significantly more sensitive to tunneling than the CMOD technique and is easier to apply than the area-average technique.

Keywords:
area-average, crack growth, cracks, CTOA, finite-element analysis, resistance curve, tunneling, unloading compliance

Paper ID: JAI12053
DOI: 10.1520/JAI12053

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Author James, MA Affiliation National Institute of Aerospace, Hampton, VA Author Newman, JC Affiliation Mississippi State University, Mississippi State, MS Title: Characterization of Crack Length Measurement Methods for Flat Fracture with Tunneling Symposium: Fatigue and Fracture Mechanics: 34th Volume, 2003-11-21
Committee: E08 on Fatigue and Fracture